FIG. 12 shows a sectional view of a conventional filter device, which is manufactured through the steps of: machining aluminum die-cast, then providing the machined die-cast with silver plating to produce frame 1, and then screwing resonant element 2 into frame 1, and finally putting lid 3 onto frame 1.
Unexamined Japanese Patent Application Publication No. H08-195607 is known as related art to the present invention.
Screwing of the resonant element to the frame produces dispersion in electrical resistance at the connected section depending on the tightening force. The dispersion will lower a Q factor of the resonator formed of the inside of the frame and the resonant element mounted in the frame. This phenomenon resultantly degrades the characteristics of the filter device, such as incurring a greater insertion loss.